The fastest way to check for malware on your PC

Run a full scan with Windows Defender, the antivirus tool built into Windows 10 and 11. Open Windows Security (search for it in the Start menu), select Virus & threat protection, then click Scan options. Choose Full scan and click Scan now. This takes 30 minutes to several hours depending on how many files you have, but it checks every file on your drive instead of just the ones you use regularly.

If you suspect active malware right now — your PC is slow, programs won't open, or you see pop-ups — restart your computer in Safe Mode before scanning. Safe Mode loads only essential Windows files, which prevents malware from running and hiding itself. To enter Safe Mode on Windows 10 or 11, hold Shift and click the power button in the Start menu, then select Restart. When the blue menu appears, select Troubleshoot, then Advanced options, then Startup Settings, then restart and press 4 for Safe Mode.

Key Takeaways

  • Windows Defender is built into Windows 10 and 11 and can scan your entire drive for malware without installing anything else.
  • A full scan checks every file on your PC and takes 30 minutes to several hours, but catches more threats than a quick scan.
  • Safe Mode prevents malware from running while you scan, which is useful if your PC is already behaving strangely.
  • If Windows Defender finds nothing but your PC still seems infected, a second opinion from Malwarebytes or a portable scanner can catch what the first tool missed.

What to do if Windows Defender finds malware

Windows Defender will quarantine anything it detects — that means it moves the file to an isolated folder where it cannot run. You do not need to do anything else; the threat is contained. When the scan finishes, Windows Defender shows you what it found and asks whether you want to remove it. Click Remove or Remove all to delete the quarantined files permanently.

Some malware hides in system files that Windows Defender cannot remove while Windows is running. If the scan report says a file needs to be removed but Windows Defender could not do it, restart your PC. Windows will attempt the removal before it fully starts up, when the malware cannot defend itself. You may see a message saying the file was removed on restart — this is normal.

When to use a second scanner

Different antivirus tools catch different malware because they use different detection methods. If your PC still shows signs of infection after a full Windows Defender scan — freezing, unexpected pop-ups, programs launching on their own — run a scan with Malwarebytes. Download the free version from malwarebytes.com, install it, and run a full scan. Malwarebytes often finds threats that Windows Defender missed, especially newer or less common malware.

Another option is a portable scanner that runs without installing anything. Kaspersky Rescue Disk and Bitdefender Rescue Disk are two examples. You download them on a different computer, write them to a USB drive, then boot your infected PC from that drive. Portable scanners run outside Windows entirely, so malware cannot interfere with them. This method is slower and more technical, but it is the most thorough check available.

How to prevent malware from coming back

Keep Windows and all your programs updated. Malware often enters through security holes in outdated software. Windows 10 and 11 update automatically by default, but make sure updates are turned on: go to Settings > Update & Security (or System > About on Windows 11) and check that updates are set to install automatically. For other programs like Firefox, Chrome, or Office, check their settings menus for an update option or let them update when they prompt you.

Be cautious about what you download and where you download it from. Malware spreads through fake software installers, email attachments, and compromised websites. Download programs only from official websites or the Microsoft Store, not from random download sites. If an email attachment seems suspicious or came from someone you do not know, do not open it. Browser extensions can also carry malware — install only extensions from the official Chrome Web Store or Firefox Add-ons, and remove any you do not recognize.

Understanding what malware actually does

Malware is a broad category that includes viruses, worms, trojans, spyware, and ransomware — each works differently. A virus copies itself to other files and spreads when you run an infected program. A trojan pretends to be legitimate software but does something harmful once installed. Spyware watches what you do and steals passwords or personal information. Ransomware locks your files and demands money to unlock them. Knowing what type of malware you have helps you understand what damage it might have done and what to check afterward.

Not every slow PC or pop-up means you have malware. Windows itself slows down over time as programs accumulate, temporary files pile up, and the hard drive fragments. Pop-ups can come from websites you visit rather than malware on your PC. But if your PC is dramatically slower than it used to be, programs crash frequently, or you see pop-ups even when you are not browsing, a malware scan is worth running.

What to check after removing malware

After a successful removal, check your browser homepage and search engine. Malware often changes these settings to redirect you to advertising sites. In Chrome, go to Settings > On startup and make sure it opens to your preferred homepage. In Firefox, go to Settings > Home and check that the homepage is what you expect. Check your search engine too: in Chrome, go to Settings > Search engine, and in Firefox, go to Settings > Search.

Look at your installed programs and remove anything you do not recognize. Go to Settings > Apps > Apps & features on Windows 11, or Control Panel > Programs > Programs and Features on Windows 10. Malware sometimes installs itself as a legitimate-looking program. If you see something unfamiliar, search for its name online before removing it — some Windows system programs have confusing names and should not be deleted.

Frequently Asked Questions

Can malware survive a Windows Defender scan?

Yes. Some malware hides in places Windows Defender does not scan by default, or uses techniques to avoid detection. If your PC still behaves oddly after a full scan, run Malwarebytes or a portable scanner for a second opinion. Different tools catch different threats.

Is Windows Defender enough, or do I need a paid antivirus?

Windows Defender is sufficient for most users if you also practice safe browsing habits — do not download from untrusted sites, do not open suspicious email attachments, and keep Windows updated. Paid antivirus tools offer extra features like real-time scanning and password managers, but they are not necessary for basic protection.

What should I do if malware locked my files with ransomware?

Do not pay the ransom. Contact the FBI's Internet Crime Complaint Center or your local law enforcement. Some ransomware has known decryption tools available online. Check the No More Ransom website (nomoreransom.org) to see if a free decryption tool exists for your specific ransomware variant.

Will scanning for malware slow down my PC?

Yes, while the scan is running. A full scan uses your hard drive and processor heavily, so your PC will be slower and noisier until it finishes. This is normal. Once the scan completes, your PC should return to normal speed. If it remains slow, the malware may have damaged system files, and you may need professional help.

Can I scan for malware on my phone?

Android phones can get malware, but iPhones rarely do because Apple controls what apps can be installed. For Android, download Malwarebytes for Android from the Google Play Store and run a scan. For iPhone, the main risk is malicious websites, not installed malware — use a browser with built-in protection like Safari or Firefox.